Obesity, the consequence of a long-term imbalance in energy homeostasis, currently afflicts one third of the American adult population. The long-range goal of this project is to identify previously unrecognized genes and pathways that participate in regulating energy homeostasis. Prior work has shown that when one gene in an energy-modulating pathway is perturbed, the expression of genes in downstream and collateral pathways is often altered. Leptin is a key regulator of both short-and long-term energy balance, and in the hypothalami of leptin deficient obese (Lepob/Lepob) mice, the expression of metabolically modulating central neuropeptides, such as agouti-related peptide (AGRP), neuropeptide Y (NPY), and peripheral hormones, such as Acrp30 are altered. These data suggest components of energy-regulated pathways can be defined by identifying genes whose expression is altered in monogenic models of obesity. The development of microarray technology, with its ability to measure the expression of thousands of genes in parallel, provides an opportunity to efficiently identify new components of energy homeostatic pathways. In this project, microarrays will be used to compare the expression of genes from four energy-regulating tissues in obese and wild-type mice. Gene expression will also be monitored in obese mice following pharmacological and metabolic interventions that are known to modify the mutant phenotype. Expression data, representing more than five million data points, will be analyzed with several established and novel algorithms to identify classes of co-regulated genes, and specifically those genes that are specifically regulated by leptin. From among these leptin-regulate genes we will use prior data and computational methods to identify gene products that encode secreted proteins. These will serve as candidates for defining unrecognized leptin regulated pathways and will be characterized functionally. Completing the proposed experiments will develop the candidate's career in several important ways: In the course of the project the candidate will gain expertise in several technologies that are of increasing importance in a "post-genomic world." He will also build a large and valuable database that correlates metabolic states with gene expression. Finally, the proposed project will provide him with new molecules and pathways to investigate, as he begins his independent career studying the molecular genetics of energy homeostasis and obesity.